Magnetic storage systems, such as a hard disk drive (HDD), are utilized in a wide variety of devices in both stationary and mobile computing environments. Examples of devices that incorporate magnetic storage systems include desktop computers, portable notebook computers, portable hard disk drives, digital versatile disc (DVD) players, high definition television (HDTV) receivers, vehicle control systems, cellular or mobile telephones, television set top boxes, digital cameras, digital video cameras, video game consoles, and portable media players.
A typical disk drive includes magnetic storage media in the form of one or more flat disks. The disks are generally formed of two main substances, namely, a substrate material that gives it structure and rigidity, and a magnetic media coating that holds the magnetic impulses or moments that represent data. Such typical disk drives also typically include a read head and a write head, generally in the form of a magnetic transducer which can sense and/or change the magnetic fields stored on the disks. Perpendicular magnetic recording (PMR) involves recorded bits that are stored in a generally planar recording layer but in a generally perpendicular or out-of-plane orientation with respect to the recording layer. A PMR read head and a PMR write head are usually formed as an integrated read/write head along an air-bearing surface (ABS). In a PMR reader, a tunnel magnetoresistance (TMR) sensor is frequently employed in the read head.
A TMR sensor generally includes a patterned TMR structure or stack having two ferromagnetic layers separated by an insulating barrier layer (e.g., MgO). One ferromagnetic layer is magnetically oriented in a fixed direction (the “pinned layer”) and the other ferromagnetic layer rotates in response to an external magnetic field (the “free layer”). The TMR sensor also typically includes a hard or soft bias (SB) layer disposed on either side of the TMR stack. The hard or soft bias layer can include a permanent or soft magnetic material and can provide a bias field along a direction perpendicular to layers of the TMR stack. The resistance of the device is dependent on the relative orientation between the two ferromagnetic layers. In a TMR read head, a sense current passes perpendicularly through layers of the TMR stack. The magnetic transitions between adjacent oppositely-directed magnetized regions cause changes in electrical resistance that are detected by the TMR sensor.
One such TMR sensor design involves use of an extended pin layer (XPL). The extended pin layer (XPL) design provides extra pinned layer and anti-ferromagnetic (AFM) layer volume to enhance pinning thermal stability of the sensor, and thereby improve device stability at smaller stripe heights (SH) and free layer track widths (FLTW). However, when this extra layer volume is incorporated with the soft bias (SB) layer, the performance of the sensor can be degraded.